In cryptography, true random numbers are used for generating encryption keys for encrypting information. Encryption keys should not be easily revealed to prevent the encrypted information from being decrypted by an unauthorized user. To reduce the risk of revealing encryption keys and thus circumventing the cryptographic application, true random numbers are used for generating such keys.
True random numbers for cryptographic applications are based on a true random process that is completely non-deterministic. This usually necessitates a hardware implementation instead of a software pseudo random implementation.
Generally, cryptographic quality random number sources include an array of ring oscillators for generating a true random number. The random phase jitter between the outputs of each ring oscillator is captured as entropy to produce a stream of random binary digits.
Portable military communication equipment, such as backpack radios, are battery operated and include cryptographic quality random number sources to provide high quality security. There is a requirement that this type of equipment consumes low power.
Unfortunately, ring oscillators draw large amounts of power, especially in high rate CMOS applications. For example, U.S. Patent application No. 2002/0156819 to Oerlmans discloses a true random number generator circuit comprising a plurality of ring oscillators connected to a linear feedback shift register. An output of the linear feedback shift register provides a random number.